This invention relates to a transparent glass board for use in document copying machines as the copying glass on which an original document is to be placed, and more particularly to an antistatic and lubricative glass board particularly suitable for use in copying machines having an automatic original document feeding means and to a method of producing the same.
Many recent document copying machines have a means for automatically feeding each sheet of an original document onto a transparent glass board placed above a light source and carrying the sheet on the glass board. Usually the original document feed means comprises a rubber belt which is rotatively driven on the glass board by several rolls turning in synchronism with a pair of document feed rolls. In operation of the copying machine the rubber belt keeps in rubbing contact with the glass board and forces each sheet of the document to slide on the glass board. Accordingly static electricity is produced by friction between the paper sheet and the glass board and also between the rubber belt and the glass board. Since both the rubber belt and the glass board are dielectric the static electricity can hardly dissipate, and consequently a large quantity of electrostatic charge accumulates between the glass board and the rubber belt. The charge offers an obstacle to smooth carriage of the paper sheets on the glass board and sometimes results in trapping of the paper sheets. Besides, dust adheres to the glass board and becomes a cause of unsatisfactory copying.
Naturally some antistatic measures have been proposed. For example, JP-UM-A 56-159345 shows providing an electroconductive and transparent coating layer to the copying glass board on its back side facing the light source and grounding the conductive layer, and JP-A 57-90668 shows a transparent antistatic coating layer on the top side of the glass board. However, the antistatic coating on the back side of the glass board hardly has the effect of ensuring smooth carriage of original document sheets on the glass board, and the antistatic coating on the top side is rather obstructive to the sliding of the paper sheets because of being inferior to glass in surface smoothness and is problematic in respect of durability.
Besides, there are proposals of providing an anti-static means or a discharge means to the paper carrying rubber belt and/or related parts of the copying machine. However, these measures involve complication of parts manufacture and a substantial rise in the cost of production.